Lower urinary tract symptoms (LUTS), common among older men, include a variety of disorders that can lead to urinary retention and complications resulting from retention. Some of the conditions falling under a LUTS diagnosis include an enlarged prostate, BPH, and bladder outlet obstruction.
The constriction of the urethra due to prostatic enlargement can be treated by the implantation of a prostatic urethral stent. The stent serves to hold the prostatic urethra open to allow urination. This is typically an interim solution used before or after corrective treatment, e.g., a stent may be implanted after radiation treatments, thermal therapy or cryosurgery to keep the urethra open while post-treatment edema subsides. In some instances, a stent may be implanted as a primary treatment.
Generally, urethral stents are tubular in shape and may be in the form of a solid tube, coiled wire, ribbon or mesh, or formed from braided filaments. Coiled stents may be designed to have at least a portion thereof with outer diameter equal to or larger than the average urethral lumen diameter, such that when expanded, the stent frictionally engages the urethra into which it has been inserted. The larger diameter coils of such stents need to be radially compressed prior to insertion into a stent delivery system, e.g., a catheter sheath, or within the urethra. After being positioned in the urethra, urethral stents are radially expanded into their final shape, typically by thermal or mechanical means, or, in the case of self-expanding stents, allowed to elastically expand when a sheath or other restraining means is removed.
Brenneman et al. (U.S. Pat. No. 5,160,341) disclose a device including a retractable sheath surrounding a rotatable rod journaled in a stationary tubular bushing. One end of the stent is mounted on the rod while the other end of the stent is fixed to the bushing so that relative rotation of the rod and bushing compresses the entire stent by coiling it more tightly. After insertion within the body, the rod and bushing are then rotated in the opposite direction to uncoil the stent to its original diameter. A shearing sleeve with a shearing edge is advanced between the rod and bushing to sever the stent from its attachment to the bushing and the rod.
In the above device, both ends of the stent are used to engage the urethra and the diameter along the entire stent length is reduced. Reduction of stent diameter results in a concomitant increase in length in the reduced region. Reduction of stent diameter along the entire stent length will therefore result in significant length increases upon diameter reduction, sizing, bunching, and consequent placement issues within the anatomy. In some coil stent designs, only an end portion of the stent has a varying diameter. It is undesirable, particularly with polymer stents, to expose a stent to unnecessary forces due to risk of plastic deformation or creep. There are also risks associated with introducing a shearing sleeve with shearing edge within the urethra e.g. breakage, contamination and/or injury. In addition, the cut ends of the stent are sharp and pose a risk of penetrating the urethra.
Yachia et al. (U.S. Pat. No. 5,246,445) disclose stents with non-uniform windings such that one or more coils along the length of the stent bulge out circumferentially. An apparatus is disclosed which fixes either end of the stent and through torquing action, radially compresses the bulges. Here again, the entire length of the stent is reduced by rotating the ends of the helical spiral in opposite directions. A small hook, ring, or ball is provided at each end of the stent for grasping it. These features diminish uninterrupted flow capacity through the stent and increase the complexity of manufacture. Counter-rotation is required to release the stent.
Limon (U.S. Pat. No. 5,476,505) discloses a stent delivery system including a catheter formed from coaxially arranged inner and outer flexible shafts, the distal ends of which have slots or apertures to engage the ends of a coiled stent. The entire length of the stent is effected by inducing tighter coiling. The device is counter-rotated to expand and release the stent.
It would therefore be desirable to be able to radially compress selected regions of a coiled stent without compressing the entire stent. Such a device can be used to facilitate placement of the stent either within a secondary insertion tool or directly within the body.